Commit c4666bfa changed s_server so that it asked libssl rather than the
underlying socket whether an error is retryable or not on the basis that
libssl has more information. That is true unfortunately the method used
was wrong - it only checks libssl's own internal state rather than both
libssl and the BIO. Should use SSL_get_error() instead.

This issue can cause an infinite loop because some errors could appear as
retryable when in fact they are not.

We now have a version of PEM_read_bytes that can use temporary
buffers allocated from the secure heap; use them to handle this
sensitive information.

Note that for PEM_read_PrivateKey, the i/o still goes through
stdio since the input is a FILE pointer. Standard I/O performs
additional buffering, which cannot be changed to use the OpenSSL
secure heap for temporary storage. As such, it is recommended
to use BIO_new_file() and PEM_read_bio_PrivateKey() instead.

Split the PEM_bytes_read_bio() implementation out into a
pem_bytes_read_bio_flags() helper, to allow it to pass PEM_FLAG_SECURE
as needed. Adjust the cleanup to properly use OPENSSL_secure_free()
when needed, and reimplement PEM_bytes_read() as a wrapper around
the _flags helper.

Add documentation for PEM_bytes_read_bio() and the new secmem variant.

The extended function includes a 'flags' argument to allow callers
to specify different requested behaviors. In particular, callers can
request that temporary storage buffers are allocated from the secure heap,
which could be relevant when loading private key material.

Refactor PEM_read_bio to use BIO_mems instead of BUFs directly,
use some helper routines to reduce the overall function length, and make
some of the checks more reasonable.

This trace option does not appear in Configure as a separate option and is
undocumented. It can be switched on using "-DOPENSSL_SSL_TRACE_CRYPTO",
however this does not compile in master or in any 1.1.0 released version.

The TLSv1.3 spec says that a server SHOULD send supported_groups in the
EE message if there is a group that it prefers to the one used in the
key_share. Clients MAY act on that. At the moment we don't do anything
with it on the client side, but that may change in the future.

perlasm/x86_64-xlate.pl: work around problem with hex constants in masm.

Perl, multiple versions, for some reason occasionally takes issue with
letter b[?] in ox([0-9a-f]+) regex. As result some constants, such as
0xb1 came out wrong when generating code for MASM. Fixes GH#3241.

SSL_CTX_use_serverinfo_ex() et al were always processing data as if it was
V2 format, even if it was V1. This bug was masked because, although we had
a test which loaded V1 serverinfo data from a file, the function
SSL_CTX_use_serverinfo_file() transparently converts V1 data to V2 before
calling SSL_CTX_use_serverinfo_ex().

Since the clang_devteam_warnings are appended to the gcc_devteam_warnings
when strict-warnings are requested, any items present in both the gcc
and clang variables will be duplicated in the cflags used for clang builds.
Remove the extra copy from the clang-specific flags in favor of the
gcc_devteam_warnings that are used for all strict-warnings builds.

gcc's -Wextra pulls in -Wold-style-declaration, which triggers when a
declaration has a storage-class specifier as a non-initial qualifier.
The ISO C formal grammar requires the storage-class to be the first
component of the declaration, if present.

Seeint as the register storage-class specifier does not really have any effect
anymore with modern compilers, remove it entirely while we're here, instead of
fixing up the order.

Interestingly, the gcc devteam warnings do not pull in -Wextra, though
the clang ones do.

clang already has it; let's flip the switch and deal with the fallout.
Exclude -Wunused-parameter, as we have many places where we keep unused
parameters to conform to a uniform vtable-like interface.
Also exclude -Wmissing-field-initializers; it's okay to rely on
the standard-mandated behavior of filling out with 0/NULL.

Approach was opportunistic in Windows context from its inception
and on top of that it was proven to be error-prone at link stage.
Correct answer is to introduce library-specific time function that
we can control in platform-neutral manner. Meanwhile we just let
be attempts to override time on Windows.

Enforcement of an SNI extension in the initial ClientHello is becoming
increasingly common (e.g. see GitHub issue #2580). This commit changes
s_client so that it adds SNI be default, unless explicitly told not to via
the new "-noservername" option.

Previously, init and finalization function for extensions are called
per extension block, rather than per message. This commit changes
that behaviour, and now they are called per message. The parse
function is still called per extension block.